The amount of heat generated within this type of electronic device has increased with an improvement in processing capability, and requires a lowering of the temperature of a hot spot more than ever to prevent a decrease in performance and damage. Furthermore, a reduction in the thickness, size, or weight is demanded to enhance portability. In order to provide a heat sink capable of satisfying such a request, for example, Japanese Unexamined Patent Application, First Publication No. 2011-3604 discloses a heat sink with low thermal resistance capable of enhancing assembling accuracy and also saving installation space. The heat sink includes a plate member corresponding to a main body, a recessed portion formed in the plate member, and a groove formed extending toward the outside from the inside of the recessed portion. A heat pipe is fit into the groove, while a thermal conductive member formed into a shape similar to that of the recessed portion is fit into the recessed portion and processed such that a surface of the thermal conductive member is aligned to a surface of the plate member corresponding to the main body so as to be flush.
The plate member corresponding to the main body of the heat sink disclosed in Japanese Unexamined Patent Application, First Publication No. 2011-3604 described above needs to have a thickness obtained by adding a thickness allowing the recessed portion to be formed such that the thermal conductive member is fit thereinto, a thickness allowing the groove to be formed in an area of the recessed portion corresponding to a so-called bottom surface such that the heat pipe is fit thereinto, and a residual thickness required for predetermined strength of the groove on a so-called bottom portion side. Accordingly, the entire thickness of the heat sink is necessarily made thicker. Moreover, because the groove has a structure for fitting thereinto the beat pipe with a cross-sectional circular shape, the thickness is made still thicker. For example, since a graphite sheet is used in the multi-function mobile phone to transfer heat within a case thereof, respective components are required to be as thin as possible. Therefore, it is difficult to employ the heat sink disclosed in Japanese Unexamined Patent Application, First Publication No. 2011-3604 for the portable electronic device.